View source for Earth:Snow squall

{{Short description|Sudden heavy snowfall accompanied with strong winds}}
[[File:Toronto lake effect frontal squall.JPG|thumb|A hybrid Frontal-Lake Effect Snowsquall hitting Toronto, Canada during rush hour.]]
{{Weather}}

A '''snow squall''', or '''snowsquall''', is a sudden moderately heavy [[Physics:Snow|snow]]fall with blowing snow and strong, gusty surface [[Earth:Wind|wind]]s.<ref>[http://www.crh.noaa.gov/dtx/glossary/s.php National Weather Service Detroit/Pontiac<!-- Bot generated title -->]</ref> It is often referred to as a [[Earth:Whiteout (weather)|whiteout]] and is similar to a [[Earth:Blizzard|blizzard]] but is localized in [[Time|time]] or in location and snow accumulations may or may not be significant.

==Types==
There are two primary types of snow squalls: lake effect and frontal.

===Lake-effect snow===
{{main article|Earth:Lake-effect snow}} 
When arctic air moves over large expanses of warmer open waters in winter, [[Astronomy:Convection|convective]] clouds develop which cause heavy snow showers due to the large amount of moisture available.  This occurs southwest of extratropical cyclones, with the curved cyclonic wind flow bringing cold air across the relatively warm Great Lakes which then leads to narrow lake-effect snow bands that can produce significant localized snowfall.<ref>{{cite web|author=B. Geerts|year=1998|url=http://www-das.uwyo.edu/~geerts/cwx/notes/chap10/lake_effect_snow.html|title=Lake-Effect Snow|access-date=2008-12-24|publisher=[[Organization:University of Wyoming|University of Wyoming]]}}</ref>  [[Earth:Whiteout (weather)|Whiteout]] conditions will affect narrow corridors from shores to inland areas aligned along the prevailing wind direction.<!--- Dead link<ref name=EC>{{Cite web
|url= http://www.on.ec.gc.ca/canwarn/winterseason-e.html#Snow%20Squall 
|title= Snow squall
|work= Snow Squall Warning
|author= Meteorological Service of Canada, Ontario Region
|publisher=Environment Canada
|date= May 17, 1999
|access-date=2010-10-04
}}</ref>--><ref name=EC-2>{{Cite web
|url= http://www.ec.gc.ca/meteo-weather/default.asp?lang=En&n=46FBA88B-1#Snow 
|title= Snow
|work=Winter Hazards
|author= Meteorological Service of Canada
|publisher=Environment Canada
|date= September 8, 2010
|access-date=2010-10-04
}}</ref><ref>{{Cite web | url= http://www.sciences360.com/index.php/what-is-lake-effect-snow-7241/ | title = What is Lake-Effect Snow | author= Cameron Scott | work= Science 360! | publisher=  RR Donnelly | access-date= October 23, 2013}}</ref> This will be enhanced when the moving air mass is [[Earth:Orographic lift|uplifted]] by higher elevations. The name originates from the Great Lakes area of [[Earth:North America|North America]], however any body of water can produce them. Regions in [[Windward and leeward|lee]] of [[Earth:Ocean|ocean]]s, such as the Canadian Maritimes could experience such snow squalls.

The areas affected by lake-effect snow are called [[Astronomy:Snowbelt|snowbelt]]s and deposition rate of many inches ([[Centimetre|centimetre]]s) of snow per hour are common in these situations. In order for lake-effect snow to form, the [[Physics:Temperature|temperature]] difference between the water and {{convert|850|mbar}} should be at least {{convert|23|F-change}}, surface temperature be around the freezing mark, the lake unfrozen, the path over the lake at least {{convert|100|km}} and the directional [[Physics:Wind shear|wind shear]] with height should be less than 30° from the surface to {{convert|850|mbar}}.<ref name=Haby>{{Cite web
|url= http://www.theweatherprediction.com/winterwx/lesnow/
|title= Lake-effect forecasting
|work= Haby's Weather Forecasting Hints 
|author= Jeff Haby 
|publisher= theweatherprediction.com
|access-date=2009-08-12
}}</ref> Extremely cold air over still warm water in early winter can even produce [[Earth:Thundersnow|thundersnow]], snow showers accompanied by [[Astronomy:Lightning|lightning]] and [[Physics:Thunder|thunder]].
{{multiple image
 | align     = center
 | width = 300

 | image1 = snowsquall20101207.jpg
 | alt1 = 
 | caption1 = Radar trace of lake-effect snow squalls off the Great Lakes from US radars.

 | image2 = snowsquall20101207 ontario.jpg
 | alt2 = 
 | caption2 = Radar image of a strong snow squall off Lake Huron in December 2010. Over 150 cm of snow from this squall, fell north of London, Ontario.<ref>{{cite news|url=https://www.cbc.ca/news/canada/snowstorm-shuts-down-london-ont-1.929437|title=Snowstorm shuts down London Ontario.|publisher=CBC|work=CBC News|date=December 8, 2010|access-date=December 13, 2017 }}</ref>
 | image3 = Lake effect snowsquall york region ontario jan08 03.jpg
 | alt3 = 
 | caption3 = A linear single banded snow squall over Southern Ontario
}}
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===Frontal snow squall===
[[File:Snowsquall line-Bourrasque neige frontal NOAA.png|thumb|upright=1.25|Frontal snow squall moving toward Boston, Massachusetts, United States]]
A frontal snow squall is an intense frontal convective line (similar to a [[Earth:Squall line|squall line]]), when [[Physics:Temperature|temperature]] is near freezing at the surface. The strong convection that develops has enough moisture to produce whiteout conditions at places which line passes over as the wind causes intense blowing snow.<ref name=EC-2/> This type of snow squall generally lasts less than 30 minutes at any point along its path but the motion of the line can cover large distances. Frontal squalls may form a short distance ahead of the surface cold front or behind the cold front in situations where there are other contributing factors such as dynamic lifting from a deepening low pressure system or a series of [[Astronomy:Trough (meteorology)|trough]] lines which act similar to a traditional cold frontal passage. In situations where squalls develop post-frontally it is not unusual to have two or three linear squall bands pass in rapid succession only separated by {{convert|25|mi}} with each passing the same point in roughly 30 minutes apart.

This is similar to a line of thunderstorms in the summer but the tops of the clouds are only {{convert|5000|to|10000|ft}}, often difficult to see on radar. Forecasting these types of events is equivalent to summer severe weather forecast for squall lines: presence of a sharp frontal trough with wind shift and low level jet of more than {{convert|30|kn}}. However, the cold dome behind the trough is at 850 mbar instead of a higher level and must be at least {{convert|-13|F}}. The presence of surface moisture from bodies of water or preexisting liquid precipitation is also a significant contributing factor helping to raise the dew point temperature and saturate the boundary layer. This saturate can significantly increase the amount of [[Physics:Convective available potential energy|convective available potential energy]] leading to deeper vertical growth and higher precipitable water levels increasing the volume of snow which can be produced by the squall. In cases where there is a large amount of vertical growth and mixing the squall may develop embedded cumulonimbus clouds resulting in lightning and thunder which is dubbed [[Earth:Thundersnow|thundersnow]].
{{Clear}}

==Dangers==

[[File:Car into ditch bad winter weather hwy 404 south near stouffville rd Jan08.jpg|thumb|Rapidly deteriorating weather conditions during snow squalls often lead to traffic accidents.]]
[[File:Snowy Higddhway 4012.jpg|thumb|Winter conditions on Ontario Highway 401 in Toronto due to a snow squall.]]

Both types of snow squalls are very dangerous for motorists, airplanes, and other travelers; even can be more dangerous than [[Earth:Blizzard|blizzard]]s.<ref>{{cite web |title=What are snow squalls and why they're more dangerous than blizzards |date=18 Dec 2021 |accessdate=19 Feb 2022 |website=CNN |author=Allison Chinchar, Meteorologist |url=https://www.cnn.com/2021/12/18/weather/weather-snow-squall-hazard-explainer/index.html}}</ref> The change in conditions is very sudden, with slippery conditions and abrupt loss of visibility due to [[Earth:Whiteout (weather)|whiteouts]], which often cause multiple-vehicle collisions. In the case of [[Earth:Lake-effect snow|lake-effect snow]], heavy amounts of snow can accumulate in short periods of time, possibly causing road closures and paralyzing cities. For instance, on January 9, 2015, a localized, heavy snow squall caused a 193-vehicle pile-up on I-94 highway near Galesburg, Michigan.<ref>{{Cite web|title = Michigan I-94 Pileup {{!}} Firefighter Nation|url = http://www.firefighternation.com/article/firefighting-operations/michigan-i-94-pileup|website = Firefighter Nation| date=May 2015 |access-date = 2015-10-09}}</ref>

==See also==
*[[Astronomy:Convection|Convection]]
*Snow shower

Warnings about lake-effect snow:

;United States
*Lake Effect Snow Advisory
*Lake Effect Snow Warning
*Severe weather terminology (United States)
*Snow squall warning

;Canada
*Snow Squall Warning
*[[Earth:Severe weather terminology (Canada)|Severe weather terminology (Canada)]]

==References==
<references />

==External links==
{{Commons|Snow}}
*[http://www.crh.noaa.gov/lmk/?n=wwfaq Winter Weather Awareness] by the US [[Earth:National Weather Service|National Weather Service]]
*[http://www.ec.gc.ca/meteo-weather/default.asp?lang=En&n=46FBA88B-1#Snow Environment Canada - Weather and Meteorology - Hazardous weather-winter hazards]
*[https://www.youtube.com/watch?v=KSLoIY3bCv8 Video of a snowsquall timelapse while driving on Highway 407 ETR in Greater Toronto]

[[Category:Weather hazards]]

de:Lake effect snow

{{Sourceattribution|Snow squall}}